xx. I ANTERIOR AND POSTERIOR EXTREMITY. 331 



Fig. 126. — Diagrammatic representation of the positions of the limbs of Mammalia 

 continued, e the anterior extremity with the same flexures as in c, but with the 

 whole limb rotated backwards. The preaxial side is external. The letters as 

 before, f the posterior extremity, with the joints bent, and the whole limb rotated 

 forwards, as in the. ordinary position of quadruped Mammals The postaxial side 

 is external, g the humerus in the same position as in e, but the fore-arm r. tated, 

 as in the ordinary position of quadruped Mammals. Whilst the preaxial side of 

 the humerus remains external, the postaxial side of the manus is now external. 

 h the anterior extremity of a Cetacean (Hyperoodou), dorsal surface, i the pos- 

 terior extremity of a Seal, dorsal surface. 



Leaving for the present the shoulder and pelvic girdles 

 out of consideration, we will next consider the adaptive 

 changes which take place in the segments of the limb 

 proper in various animals. These will be best understood 

 by dividing them into stages (all of which are represented 

 in the diagram), though it is not meant to imply that the 



